Electrochemical preparation of standard gas mixtures using solid-state electrolyte membrane

Abstract

A novel electrochemical method of preparation of standard gas mixtures for calibration of gas-analytical equipment with O2, H2 and CO was elaborated. Utilization of solid state electrolyte membrane allows to perform a nearly 100%-efficient electrochemical generation or conversion of the analyte and avoid some problems typical for liquid electrolytes, such as solvent evaporation and condensation at the inner walls of the gas tubes or deviations from the Faraday’s law. Analysis of uncertainties associated with the calibration procedure showed that the lowest systematic errors are achieved when the calibrant is generated during the electrolysis (i.e. anodic evolution of oxygen or cathodic generation of CO), and the major uncertainties are associated with operation of the flow controllers. For calibration with H2, where the calibrant is partially converted during the electrochemical process, the total uncertainty is essentially determined by molar fractions of the components in H2-Ar mixture, instrumental errors of the equipment, primarily by precision of mass-flow controllers or stability of the gas flow, and the initial flow rate of the calibrant-containing gas mixture. The relative total errors of calibration with oxygen are assessed to be 5–6%; similar uncertainties were calculated for analysis of oxygen content in standard gas mixtures by chromatography using the electrochemical method of calibration.